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DeKalb Pfizer Genetics, 3100 Sycamore Rd., DeKalb, IL 60115
* Corresponding author.
Genetic vulnerability of corn (Zea mays L.) has increased repeatedly since the growing of hybrid corn, single cross hybrids, and popular hybrids. We definite genetic vulnerability as the potential susceptibility of a crop to future attack by some biological or environment stress due to growing large numbers of a uniform biotype over large geographical areas. Genetic diversity, which usually decreases genetic vulnerability, has lacked a good method for measurement. The purpose of this study was to develop and test a method for measuring genetic diversity of corn and to assess genetic vulnerability in the U.S. Corn Belt by comparing genetic diversity of popular hybrids between two major and seed companies. Genetic diversity was estimated by the formula: GD = 1-[(H-C)/(H-S)], where GD equals genetic diversity, H equals the average performance of the two hybrids, C equals the hybrid-by-hybrid cross, and S equals the average of the selfed hybrids. The method assumes heterosis is caused by some degree of dominance and epistasis is absent. A higher than average performing cross of two hybrids (less inbreeding depression) indicates more genetic diversity between the hybrids while lower than average performance of the cross (more inbreeding depression) indicates less diversity. Data were collected for grain yield, time to flower, grain moisture, and plant height on five popular hybrids from each of two major seed companies. Results for yield provided more precise estimates of GD than other performance traits measured. Genetic diversity averaged 0.74 and ranged from 0.17 to 1.37 and 0.28 to 1.12 among hybrids within companies. The GD estimate for the two most popular hybrids of 1985, 3732 and T1100 was 0.94. Our results help those needing a method to measure genetic diversity and should also encourage those concerned about genetic vulnerability in corn.
Key Words: Crop disaster • Genetic vulnerability • Heterosis • Inbreeding depression • Performance testing • Risk assessment
Received for publication May 28, 1987.
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